feat(vault): add owner-only sweep_idle_balance with settlement/revenue_pool routing

[elijah4196]

feat(vault): add owner-only sweep_idle_balance with settlement/revenue_pool routing

Summary

Operators occasionally need to move surplus USDC out of the vault into the
settlement contract or revenue pool without going through deduct, which encodes
per-call business logic. This PR adds a dedicated sweep_idle_balance flow with
full auth, pause, and balance guards plus event coverage.

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Changes

contracts/vault/src/lib.rs

• SweepDestination enum (#[contracttype]) — Settlement | RevenuePool
• SweptEventData struct (#[contracttype]) — destination, amount, new_balance
• sweep_idle_balance(env, owner, to, amount) entrypoint:
  • Owner-only (owner.require_auth() + explicit owner check)
  • Blocked when paused (require_not_paused)
  • Resolves destination address from StorageKey::Settlement or StorageKey::RevenuePool; returns VaultError::DestinationNotConfigured (code 37) if not set
  • Follows CEI pattern: balance decremented and event emitted before the external token transfer
  • Bumps instance storage TTL on every successful call
• VaultError::DestinationNotConfigured = 37 — new error code

contracts/vault/src/test_sweep_idle_balance.rs (new)

13 tests covering all acceptance criteria:

Test	Covers
sweep_rejects_non_owner	Auth — non-owner rejected with Unauthorized
sweep_requires_owner_auth	Auth — no mock → panics
sweep_blocked_when_paused	Pause guard
sweep_settlement_not_configured	DestinationNotConfigured for settlement
sweep_revenue_pool_not_configured	DestinationNotConfigured for revenue pool
sweep_zero_amount_rejected	AmountNotPositive
sweep_negative_amount_rejected	AmountNotPositive
sweep_exceeds_balance_rejected	InsufficientBalance
sweep_partial_to_settlement	Happy path — settlement, USDC transferred, balance decremented
sweep_partial_to_revenue_pool	Happy path — revenue pool
sweep_full_balance_drain	Amount == full balance → tracked balance 0
sweep_emits_event	swept event shape: destination, amount, new_balance
sweep_balance_consistency_after_multiple_sweeps	Multi-sweep accounting consistency

contracts/vault/src/events.rs

• Added event_swept_bytes snapshot test asserting byte-level identity of "swept" topic

EVENT_SCHEMA.md

• Added full swept event specification with field table, two JSON examples, and indexer notes
• Added swept row to the indexer quick-reference table
• Added version history entry

contracts/vault/STORAGE.md

• Added sweep_idle_balance to the TTL-bump entrypoints list
• Added sweep_idle_balance row to the Core Vault Operations table
• Added version 1.3 history entry

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Acceptance criteria

• Owner-only auth verified by test (sweep_rejects_non_owner, sweep_requires_owner_auth)
• Emits swept event with (destination, amount, new_balance) payload (sweep_emits_event)
• Updates meta.balance consistently with the on-ledger USDC move (sweep_balance_consistency_after_multiple_sweeps)

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Testing

cargo test -p callora-vault sweep_idle_balance

All 13 tests in test_sweep_idle_balance.rs pass.

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closes #415

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